1. Technical Field
The disclosure is generally related to haptic systems employing force feedback.
2. Description of the Related Art
Touch, or haptic interaction is a fundamental way in which people perceive and effect change in the world around them. Our very understanding of the physics and geometry of the world begins by touching and physically interacting with objects in our environment. The human hand is a versatile organ that is able to press, grasp, squeeze or stroke objects; it can explore object properties such as surface texture, shape and softness; and it can manipulate tools such as a pen or wrench. Moreover, touch interaction differs fundamentally from all other sensory modalities in that it is intrinsically bilateral. We exchange energy between the physical world and ourselves as we push on it and it pushes back. Our ability to paint, sculpt and play musical instruments, among other things depends on physically performing the task and learning from the interactions.
Haptics is a recent enhancement to virtual environments allowing users to “touch” and feel the simulated objects with which they interact. Haptics is the science of touch. The word derives from the Greek haptikos meaning “being able to come into contact with.” The study of haptics emerged from advances in virtual reality. Virtual reality is a form of human-computer interaction (as opposed to keyboard, mouse and monitor) providing a virtual environment that one can explore through direct interaction with our senses. To be able to interact with an environment, there must be feedback. For example, the user should be able to touch a virtual object and feel a response from it. This type of feedback is called haptic feedback.
In human-computer interaction, haptic feedback refers both to tactile and force feedback. Tactile, or touch feedback is the term applied to sensations felt by the skin. Tactile feedback allows users to feel things such as the texture of virtual surfaces, temperature and vibration. Force feedback reproduces directional forces that can result from solid boundaries, the weight of grasped virtual objects, mechanical compliance of an object and inertia.
Conventional haptic devices (or haptic interfaces) are typically mechanical devices that mediate communication between the user and the computer. Haptic devices allow users to touch, feel and manipulate three-dimensional objects in virtual environments and tele-operated systems. Most common computer interface devices, such as basic mice and joysticks, are input-only devices, meaning that they track a user's physical manipulations but provide no manual feedback. As a result, information flows in only one direction, from the peripheral to the computer. Haptic devices are input-output devices, meaning that they track a user's physical manipulations (input) and provide realistic touch sensations coordinated with on-screen events (output). Examples of haptic devices include consumer peripheral devices equipped with special motors and sensors (e.g., force feedback joysticks and steering wheels) and more sophisticated devices designed for industrial, medical or scientific applications (e.g., PHANTOM™ device).
Haptic interfaces are relatively sophisticated devices. As a user manipulates the end effecter, grip or handle on a haptic device, encoder output is transmitted to an interface controller. Here the information is processed to determine the position of the end effecter. The position is then sent to the host computer running a supporting software application. If the supporting software determines that a reaction force is required, the host computer sends feedback forces to the device. Actuators (motors within the device) apply these forces based on mathematical models that simulate the desired sensations. For example, when simulating the feel of a rigid wall with a force feedback joystick, motors within the joystick apply forces that simulate the feel of encountering the wall. As the user moves the joystick to penetrate the wall, the motors apply a force that resists the penetration. The farther the user penetrates the wall, the harder the motors push back to force the joystick back to the wall surface. The end result is a sensation that feels like a physical encounter with an obstacle.
General-purpose commercial haptic interfaces used today can be classified as either ground based devices (force reflecting joysticks and linkage based devices) or body based devices (gloves, suits, exoskeletal devices). The most popular design on the market is a linkage based system, which consists of a robotic arm attached to a grip (usually a pen). A large variety of linkage based haptic devices have been patented (examples include U.S. Pat. Nos. 5,389,865; 5,576,727; 5,577,981; 5,587,937; 5,709,219; 5,828,813; 6,281,651; 6,413,229; and 6,417,638).
An alternative to a linkage based device is one that is tension based. Instead of applying force through links, cables are connected a point on a “grip” in order to exert a vector force on that grip. Encoders can be used to determine the lengths of the connecting cables, which in turn can be used to establish position of the cable connection point on the grip. Motors are used to create tension in the cables.
Predating Dr. Seahak Kim's work on the SPIDAR-G, Japanese Patent No. 2771010 and U.S. Pat. No. 5,305,429 were filed that describe a “3D input device” as titled in the patent. This system consists of a support means, display means and control means. The support means is a cubic frame. Attached to the frame are four encoders and magnetic switches capable of preventing string movement over a set of pulleys. The pulleys connect the tip of each encoder to strings that are wound through the pulleys. Each string continues out of the pulley to connect with a weight that generates passive tension in the string. The ON/OFF magnetic switches allow the strings to be clamped in place on command from the host computer. The strings connect to the user's fingertip, which are connected to the weights through the pulleys. The user moves his or her fingertip to manipulate a virtual object in a virtual environment, which is displayed through a monitor. As the user moves his or her fingertip, the length of the four strings change, and a computer calculates a three-dimensional position based on the number of pulses from the encoder, which indicate the change of string length between the pulleys and the user's finger. If the three-dimensional position of the fingertip is found to collide with a virtual object as determined by a controlling host computer, then the ON/OFF magnetic switch is signaled to grasp and hold each string so that movement is resisted. Forces are not rendered in a specific direction, but resistance in all directions indicates that a user has contacted a virtual object. When the fingertip is forced outside the boundary of a virtual object, the magnetic switch is turned off to release the strings. The user is then able to move his or her finger freely.
A system that combines virtual reality with exercise is described in U.S. Pat. No. 5,577,981. This system uses sets of three cables with retracting pulleys and encoders to determine the position of points on a head mounted display. Using the lengths of the three cables, the position of the point in space is found. Tracking three points on the helmet (nine cables) allows head tracking of six degrees of freedom. Three cables attached to motor and encoders are also used to control the movement of a boom that rotates in one dimension through a vertical slit in a wall. The boom also has a servomotor at its end, about which the boom rotates. It is claimed that the force and direction of force applied by the boom can be controlled via the cables, servo motor and computer software, but no details are provided for how this is accomplished. U.S. Pat. Nos. 5,305,429 and 6,630,923 describe two cables based haptic interface devices.
Haptic interface devices can be used in a variety of fields for a variety of purposes. One field where haptic interface devices are currently employed is in simulating medical procedures for training medical personnel such as doctors in new techniques and/or for allowing medical personnel to practice old techniques. The practice of old or new techniques via a haptic interface device is especially important when the techniques are complicated and/or inherently risky to patients. Normally, conventional haptic interface devices can be large and for all practical purposes non-portable. Thus, hospitals and organizations that use a conventional haptic interface device normally dedicate a room for the conventional haptic interface device. This means that persons wanting or needing to use a conventional haptic interface device must go to the dedicated room in order to practice on the conventional haptic interface device, which can be very inconvenient to the persons wanting or needing to use the conventional haptic interface device. A problem with conventional haptic interface devices is that they may be under-utilized due to the inconvenience of the user having to go to the dedicated room. Another problem is that hospitals and other organizations might not have the resources for housing the conventional haptic interface devices. Thus, there exists a need to overcome the aforementioned deficiencies.